1. Field of the Invention
The present invention relates to a read head with improved lead layers and, more particularly, to lead layers that have planar high and low resistance lead layer portions wherein the high resistance lead layer portions have improved dimensions and performance.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arn biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation-stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. Accordingly, the first and second gap layers are constructed as thin as possible without shorting the lead layers to the first and second lead layers. High linear density results in more bits being read by the read head per length of magnetic track passing by the read head on the rotating disk.
Each of the first and second leads has a high resistance lead layer and a low resistance lead layer which means that the resistance of the high resistance layer is higher than the resistance of the low resistance layer. Each high resistance lead layer is a material that is resistant to corrosion since it has an edge exposed at the air bearing surface. The high resistance lead layer typically includes a film made of tantalum (Ta). Each low resistance lead layer is corrosive, but this is of no consequence since it is protected from the outside environment by being recessed in the head. The low resistance lead layer typically includes a film made of copper (Cu) or gold (Au).
The high resistance layer has multiple films. One of the films is the Ta film for conducting a sense current through the read sensor. Another one of the films is a hard bias film for longitudinally biasing the read sensor so that it is magnetically stabilized to prevent Barkhausen noise. In the past each high resistance lead layer extended from a respective side edge of the read sensor in a lateral direction (parallel to the ABS) before it extended back into the head to make contact with the low resistance lead layer. The longer the extension of the high resistance lead layer the thicker the high resistance lead layer has to be in order to maintain its resistance at an acceptable level. When the resistance gets too high the read head is damaged by heat. When the extension of the high resistance lead layer is made thicker in order to keep its resistance down planarization between the top surfaces of the read sensor layer and the high resistance lead layers is degraded.
The read sensor is bounded by a front edge at the ABS, first and second side edges that extend perpendicular to the ABS and a back edge that is spaced from the ABS and that defines a stripe height of the read head. Each high resistance lead layer has a forward edge that makes contact with a respective one of the first and second edges of the read sensor and is described in commonly assigned U.S. Pat. No. 5,018,037 which is incorporated by reference herein. This type of connection is referred to in the art as a contiguous junction. When the high resistance lead layers are thickened in order to reduce resistance their top surfaces are elevated with respect to the top surface of the read sensor. This causes a step adjacent each side edge of the read sensor. Unfortunately, these steps are replicated through the second gap layer and the second shield/first pole piece layer all the way to the write gap layer of the write head which may cause the write gap layer to be curved. The curved write gap layer causes the write head to write curved bits (magnetic signals) on the rotating track. When the straight across read head reads these curved bits it progressively loses magnetic intensity from a center of the bit toward outer edges of the track. Accordingly, there is a strong felt need to promote planarization of the read sensor and the high resistance leads so as to reduce write gap curvature.
We sought a method to construct the lead layers that would promote planarization between the read sensor and the high resistance lead layers at the ABS. One method investigated constructs the high resistance lead layers before defining a stripe height of the sensor by milling. In this method read sensor material layer is deposited over an entire wafer. A first mask is formed that has openings at the high resistance lead layer sites which extend to the first and second side edges of the read sensor. Read sensor material is milled out at the high resistance lead layer sites and the high resistance lead layer material is deposited to form first and second high resistance lead layers at the high resistance lead layer sites that make contiguous junctions with the first and second side edges of the read sensor. This establishes the track width of the read. Track width density (number of tracks per inch of the magnetic disk) times the aforementioned linear density is the areal density of the read head. Increasing the areal density increases the bit density (number of bits per square inch of the magnetic medium) of the disk drive. The first mask is removed and a second mask is formed that covers the read sensor and the high resistance lead layers. All exposed read sensor material is then milled away to define the back edge and stripe height of the read sensor. The stripe height is important in establishing the magnetics of the read sensor. The second mask is then removed and a third mask is formed that has openings at low resistance lead layer sites. Low resistance lead layer material is then deposited that forms first and second low resistance lead layers that overlap and engage the first and second high resistance lead layers. The third mask is then removed.
Unfortunately, the aforementioned method alters the high resistance lead layers when the stripe height of the read sensor is defined. Since the second mask must be slightly inboard of the outer edges of the high resistance layers in order to ensure complete removal of unwanted read sensor material, an outer edge portion of each high resistance lead layer is subjected to milling. Reduction of the high resistance layers due to this milling requires that the thickness of the high resistance layers be increased as deposited in order to satisfy the resistance requirements. As stated hereinabove, thicker high resistance leads results in increased write gap curvature. Accordingly, there is a strong felt need to provide a method of making the read sensor leads that will not contribute to thicker high resistance lead layers.
Instead of extending the high resistance lead layers laterally before making a turn to connect to the low resistance lead layers the present invention extends the high resistance lead layers straight back into the head from each of the first and second side edges of the read sensor. This lessens the length of the each of the high resistance lead layers so that they do not have to be made thicker to satisfy the resistance requirements. Accordingly, a lateral width of each high resistance lead portion along the ABS and a thickness thereof are chosen so as to minimize the thickness while satisfying the resistance requirements. First and second methods of construction are provided which employ novel aspects of making the read heads. Each method employs a different set of masking steps, however, the second method provides an improvement over the first method regarding the prevention of shorts between the lead layers and the second shield layer.
In the first method the high resistance lead layers are constructed last. After depositing read sensor material over a wafer a first mask is formed that has openings at the low resistance lead layer sites. After milling the read sensor material from the low resistance lead layer sites low resistance lead layer material is deposited. This forms the first and second low resistance lead layers. A second mask is then formed that covers the read sensor site and the low resistance lead layers. The second mask has a large opening that exposes all unwanted read sensor material and has an edge that is located at the desired back edge (stripe height) of the read sensor. The read sensor material is milled away and the second mask is removed leaving the read sensor with a desired stripe height. Next, the third mask is formed with openings at the first and second high resistance lead layer sites. After removing read sensor material at the first and second high resistance lead layer site high resistance lead layer material is deposited to form the first and second high resistance lead layers. The third mask is then removed. The high resistance lead layers are now complete and are more predictable since they have not been subjected to processing steps in the construction of the low resistance lead layers and the read sensor.
A special step is employed after forming the second mask and milling away the unwanted read sensor material. The second mask covers the read sensor site as well as a portion of read sensor material layer adjacent first and second edge sites of the read sensor site. The second mask cannot define the first and second edges of the read sensor since this is the function of the third mask which implements a contiguous junction between the high resistance lead layers and the side edges of the read sensor. Accordingly, the second mask leaves some unwanted read sensor material adjacent each edge of the read sensor site. When the third mask is formed the openings therein expose this unwanted read sensor material as well as a portion of the first gap layer where unwanted read sensor material was removed during the second masking step. It should be noted that if each opening in the third mask did not expose some of the first gap layer there would be no assurance that all read sensor material was removed except at the read sensor site. Without protection the first gap layer is exposed to a developer for patterning the third mask and an ion milling process after patterning the third mask. The developer and the ion milling will seriously damage the insulating quality of the first gap layer. This problem has been overcome in the present invention by depositing an insulation refill material after milling has occurred in the second masking step. The insulation refill material will now be adjacent the unwanted read sensor material in each opening of the third mask. Accordingly, when milling is implemented the milling mills insulation refill material as well as the read sensor material. In the preferred embodiment the thickness of the refill insulation material is designed so that the refill insulation material and the read sensor material are consumed at the same time in each of the openings of the third mask at the high resistance lead layer sites. This then exposes the first gap layer with no damage. The high resistance lead layer material can then be deposited in the openings in the third mask. The third mask is then removed.
Unfortunately a step occurs when the high resistance lead layers overlap the low resistance lead layers in order to make connection therewith. When the low resistance lead layers are constructed with the first masking step they have forward edges that are recessed from the back edge of the sensor in a direction away from the ABS. This is necessary because the low resistance lead layers cannot protrude into the first and second side edge regions of the sensor where the high resistance lead layers make a contiguous junction with the first and second side edges of the sensor. Accordingly when the third masking step is employed for making the high resistance lead layers each high resistance lead layer must climb up a step of a respective low resistance lead layer. The problem with this is that when the bi-layer photoresist for the third mask is constructed on the wafer, it tends to planarize which causes the under cut of the bi-layer photoresist to be smaller in height. This causes the sputtered material of the high resistance lead layers to be sputter deposited on the side walls of the upper layer of the bi-layer photoresist so that when the bi-layer photoresist is removed the high resistance lead layers have upwardly projected protrusions which is referred to as fencing. When the second gap layer is formed this fencing may protrude through the second gap layer contacting the second shield layer to cause shorts between the lead layers and the second shield layer. The second method described hereinbelow obviates this problem.
In the second method of construction after constructing the first shield layer and the first gap layer a read sensor material layer is formed over the entire wafer on the first gap layer. The first mask is then employed for defining the back edge or stripe height of the sensor. The first mask also extends back into the head to cover the sensor material layer where first and second lead layer sites are located. After ion milling down to the first gap layer the refill insulation material is deposited for the same purpose as described in the first method, namely preventing damage to the first gap layer in subsequent processing steps. The first mask is then removed leaving sensor material at the sensor site, on each side of the sensor site and in first and second recessed portions where the first and second lead layer sites are located. Surrounding the sensor material layer is refill insulation material on top of the first gap layer. Next, a second mask is formed which has first and second openings at first and second lead layer sites wherein the first and second openings encompass and are spaced from the first and second low resistance lead layer sites have edges that define first and second edges of the sensor. Refill insulation material in the spaces between the second mask and the sensor material layer covers and protects first gap layer portions where the first and second low resistance lead layers are to be subsequently constructed. The refill insulation material in the spaces protects the first gap layer portions from the developer of the second mask as well as the next step of ion milling. Next, ion milling is implemented to remove all material in the first and second openings of the second mask, which material is sensor material and refill insulation material. This ion milling also defines the first and second side edges of the sensor to define its track width. Next, the high resistance lead layer material is deposited in the first and second openings of the second mask making contiguous junctions with the first and second side edges of the sensor. Next, the second mask is removed leaving the high resistance leads making contiguous junctions with the sensor and extending back into the head encompassing sites where the first and second low resistance lead layers are to be subsequently constructed. Optionally, the refill insulation material may be removed at this stage by any suitable means such as a selective process which will remove the refill material but not remove the high resistance lead layer material, the sensor or the first gap layer. Next, the third mask is formed with openings at first and second low resistance lead layer sites which have perimeters inboard of the recessed portions of the first and second high resistance lead layers. It should be noted at this point that there has been no step coverage between the high resistance and low resistance lead layers since the recessed portions of the high resistance lead layers provide platforms for the low resistance lead layers formed by the third mask. The low resistance lead layers are then deposited covering the high resistance lead layers and the third mask is removed. The second gap layer and the second shield layer can then be formed followed by formation of the write head.
An object of the present invention is to provide a read head with improved high resistance lead layers at the ABS.
Another object is to provide a minimal extension of the high resistance lead layers of a read head so that their thickness does not have to be increased to satisfy resistance requirements.
A further object is to provide a read head with first and second lead layers that are more planarized with respect to a read sensor.
Still another object is to provide a read head that does not adversely impact the straightness of a write gap layer of a write head.
Still a further object is to provide a method of making first and second lead layers of a read head that promotes planarization of the lead layers and a read sensor.
Still another object is to provide a method of making first and second lead layers of a read head wherein both lead layers are completely flat and are not required to make step coverages with respect to one another.